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Insulated lightweight building components generally need a vapor retarder at the warm side in order to avoid an excess of inter-stitial condensation. Depending on the climate, the retarder has to be installed at the interior or exterior, sometimes at both sides of the assembly in mixed climates. However, a retarder not only diminishes the interstitial condensation, it also reduces the drying potential of the assembly, thus increasing the risk of damage, e.g., due to moisture loads caused by imperfections in the construction. By adapting its vapor permeability according to the ambient conditions in a range between 0.7 perm and 36 perm, the smart retarder opens up its pores when good drying conditions for the assembly prevail. The principle of this retarder is explained and the effect on the moisture tolerance of building components is shown in comparison to conventional retarders by field tests of unvented cathedral ceilings in heating climates. Furthermore, its performance is also assessed by simple interstitial condensation and evaporation considerations on which many building codes are based. The results show that the smart retarder effectively reduces the moisture damage risk of building assemblies in heating climates.

AUTHOR: Hartwig M. Kuenzel, Ph.D.
CITATION: Thermal Performance of the Exterior Envelopes of Buildings VII
KEYWORDS: December, Florida, 1998
YEAR: 1998

Citation: Thermal Performance of the Exterior Envelopes of Buildings VII